In gas turbine engines, air is compressed at an initial stage, then is heated in combustion chambers, and the hot gas so produced passes to a turbine that, driven by the hot gas, does work which may include rotating the air compressor.
In a typical industrial gas turbine engine a number of combustion chambers combust fuel and hot gas flowing from these combustion chambers is passed via respective transitions (also referred to by some in the field as ducts or transition pieces) to respective entrances of the turbine. More specifically, a plurality of combustion chambers commonly are arranged radially about a longitudinal axis of the gas turbine engine, and likewise radially arranged transitions respectively comprise outlet ends that converge to form an annular inflow of hot gas to the turbine entrance. Each transition exit is joined by a seal to one or more turbine components, the latter known in various designs as row 1 vane segments. Adjacent component growth variances due to thermal expansion, thermal stresses, and vibrational forces from combustion dynamics all affect design criteria and performance of such a seal, referred to herein as a transition-to-turbine seal. Consequently, the design of such seal has presented a challenge that resulted in various approaches that attempt to find a suitable balance between seal cost, reliability, durability, installation and repair ease, performance, and effect on adjacent components.
For example, U.S. Pat. No. 5,265,412, issued Nov. 30, 1993 to Bagepalli et al., teaches the use of flexible brush seals that are positioned between the transition and turbine entrance. An exemplary embodiment comprises a sealing cap solidly affixed to a first stage nozzle of the turbine, extending over a brush seal positioned at the end of the transition and an extending flexible brush radially outward to contact the adjacent sealing cap. An alternative embodiment provides the brush on the turbine component and the sealing cap extending from the transition (see FIG. 8). U.S. Pat. No. 5,749,218, issued May 12, 1998 to Cromer and Potter, illustrates a prior art flexible seal, one end of which fits into a U-shaped slot in the transition. The other end engages the first stage of the turbine. Recognizing a problem of wear in the U-shape slot, the inventors of U.S. Pat. No. 5,749,218 solve this problem by inserting an insert into the slot that is comprised of a harder alloy than the metal forming the slot. This is stated to increase the effective wear resistance of the slot.
Also, FIG. 3 of U.S. Pat. No. 6,442,946, issued Sep. 3, 2002 to Kraft et al., depicts a prior art seal that engages a vertical flange on a transition and inserts into a groove in an adjacent transition member. The engagement about the transition appears to be a relatively thick casting that would “float,” and is not indicated as spring-loaded. In contrast, U.S. Pat. No. 6,547,257, issued Apr. 15, 2005 to Cromer, discloses a transition piece seal comprising a transition piece seal support having a first flange for supporting a transition piece seal, and a second flange adapted for mounting in an adjacent nozzle, and a spring seal element itself comprising a mounting flange adapted to engage the second flange and a flex portion, embodied as spring seal elements, having a free edge adapted to engage the nozzle's forward face. In an exemplary embodiment, a cloth seal extends from the first flange into an upstanding groove or channel formed by flanges of a transition. The spring seal elements are stated to provide two separating sealing interfaces, one along the nozzle's forward face, and the other resulting from spring-biased downward pressure upon the second flange which is inserted into a slot in the nozzle.
Further, regarding wear and overall performance, it is appreciated that the initial close tolerances of newly installed “floating” type seals are not retained over the component life. Wear results in larger gaps, through which compressed air enters the hot gas path. Such air loss is expected to reduce performance efficiency and increase No, emissions. Also, for turbine designs that utilize a plurality of row 1 vane segments per transition, the independent movement of adjacent row 1 vane segments increases the dynamic challenges placed on a transition-to-turbine seal for such configuration.
Accordingly, each of the above and other known approaches to transition-to-turbine seals has one or more factors that argue against its use in advanced-design gas turbine engines that seek to attain greater performance and emissions efficiencies. Thus, there remains a need for an improved transition-to-turbine seal.